The article "Gold-lacquer printing supersedes metal bronzing," published on pages 42-43 of the February, 1993 edition of the periodical FlexoDruck [FlexoPrinting] describes a printing process wherein a gold-lacquer ink is processed in a multi-color offset printing machine having two so-called lacquer towers. One of the lacquer towers used in this process was converted from a flexographic printing unit and used a flexographic printing plate for coating with a conventional lacquering technique. In comparison with conventional lacquer metering, the article points out that a chamber doctor could be used with the apparatus.
DE 3,906,648 A1 illustrates an applicator unit for use with either high-viscosity, oil-containing layers or low-viscosity, water-soluble layers. The disclosed applicator unit is designed as a lacquering device which can be used either as an offset typographic unit or as an intaglio printing unit. If used as an offset typographic unit, the design starts from a structured scoop roller corresponding to a doctor blade. If used as an intaglio printing unit, the design starts from an applicator roller and a structured form cylinder corresponding to a doctor blade. The typographic printing unit consists of 1) a scoop roller whose surface is engaged by a doctor blade and whose surface profile includes small cups; 2) a transfer roller engaged by smoothing rollers; and 3) a form cylinder equipped with a typographic printing form.
DE 4,122,990 A1 discloses a bronze and fancy-effect printing ink and a process for producing a bronze and fancy-effect print. More specifically, it describes a water-dilutable printing ink having high viscosity and a high pigment fraction. This ink is processed with the lacquer unit of an offset machine or from a flexographic printing unit. A short processing path with few color splits is described as an advantage of this approach.
DE 3,046,257 C2 describes an apparatus having a lacquer-supply container and a scoop roller. In this apparatus, the lacquer picked up by the scoop roller is fed to an applicator roller in a metered manner. Two doctor rollers can be thrown onto the scoop roller and a doctor blade can be thrown onto the metering roller for stripping off lacquer.
DE 3,427,898 C1 discloses an apparatus which meters lacquer by way of a lacquer gap formed between two rollers.
The devices taught by DE 3,046,257 C2, DE 3,906,648 A1, and DE 3,427,898 C1 share at least one disadvantage. When used to process fluids having high viscosities such as fluids with viscosities from approximately 0.1 to 2 Pas, so-called lacquer nests can occur. Specifically, the yield points of these high viscosity fluids can result in faults in the fluid flows which could in turn lead to lacquer nests where lacquer easily dries in an undesirable manner.
DE 3,614,582 A1 discloses a so-called chamber doctor for applying a coating mass onto a coating roller. In this disclosure, at least two doctor blades bearing on a roller form a chamber for receiving a coating mass. One disadvantage of this structure is that the coating mass, which is fed to the chamber under pressure, can escape only by way of the doctor gap. A further disadvantage is that the excess coating mass is returned via a pressureless space. Finally, when fluids of higher viscosity are used, deposits can build up on the doctor blades and lead to printing faults.